This application makes reference to, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for MEMORY SYSTEM FOR IMPROVING DATA INPUT/OUTPUT PERFORMANCE AND METHOD OF CACHING DATA RECOVERY INFORMATION earlier filed in the Korean Industrial Property Office on the 16th of Sep. 1996, and there duly assigned Serial No. 40202/1996.
1. Field of the Invention
The present invention relates to a memory system such as a redundant array of inexpensive disks (RAID) and, more particularly, to a redundant arrays of inexpensive disks capable of providing high data input/output performance and a method of caching data recovery information using the redundant array of inexpensive disks.
2. Description of the Related Art
A high technology computer system depends considerably on its central processor unit (CPU) and input/output subsystem to increase overall system performance. While the information processing speed of the CPU has been dramatically improved in recent years because of VLSI technology, the performance of the input/output subsystem has not improved as desired. This increases the time required to access data in the memory system. Furthermore, since the cost of restoring data has increased when an error is generated in the input/output subsystem, an input/output subsystem having excellent performance and reliability is needed. As a solution to this, a disk array system known as a redundant array of inexpensive disks (RAID) constructed of a number of relatively small capacity disk drives has been proposed as a low cost alternative to a single large expensive disk for storing digital information.
RAID systems are now commercially available as cost effective mass storage providing reliable and continuous services to a host computer or network file server. The theory of RAID is to use relatively inexpensive disks, which may individually have a higher chance of failure than expensive disks, and compensating for this higher failure rate by adding redundancy by creating and storing parity blocks to facilitate recovery from a disk failure. Reports on the performance and reliability of disk arrays are presented in xe2x80x9cA Case For Redundant Arrays Of Inexpensive Disks(RAID)xe2x80x9d by D. Patterson, G. Gibson, and R. H. Kartz, at Report No. UCB/CDS87/89, December 1987, Computer Science Division (EECS), University of California, Berkeley, Calif. 94720. Exemplars of contemporary RAID systems are disclosed in U.S. Pat. No. 5,257,367 for Data Storage System With Asynchronous Host Operating System Communication Link issued to Goodlander et al., U.S. Pat. Nos. 5,367,669 and 5,455,934 for Fault Tolerant Hard Disk Array Controller issued to Holland et al., U.S. Pat. No. 5,418,921 for Method And Means For Fast Writing Data To LRU Cached Based DASD Arrays Under Drivers Fault Tolerant Modes issued to Cortney et al., U.S. Pat. No. 5,463,765 for Disk Array System, Data Writing Method Thereof, And Fault Recovering Method issued Kakuta et al., U.S. Pat. No. 5,485,598 for Redundant Disk Array (RAID) System Utilizing Separate Cache Memories For The Host System And The Check Data issued to Kashima et al., U.S. Pat. No. 5,522,032 for RAID Level 5 With Free Blocks Parity Cache issued to Franaszek et al., U.S. Pat. No. 5,530,948 for System And Method For Command Queuing On RAID Levels 4 And 5 Parity Drives issued to Islam, U.S. Pat. No. 5,579,474 for Disk Array System And Its Control Method issued to Kakuta et al., U.S. Pat. No. 5,640,506 for Integrity Protection For Parity Calculation For RAID Parity Cache issued to Duffy, and U.S. Pat. No. 5,636,359 for Performance Enhancement System And Method For A Hierarchical Data Cache Using A RAID Parity Scheme issued to Beardsley et al.
As generally discussed in the Patterson report and subsequent contemporary RAID systems, the large personal computer market has supported the developement of inexpensive disk drives having a better ratio of performance to cost than single large expensive disk systems. The number of input/outputs (I/Os) per second per read/write head in an inexpensive disk is within a factor of two of the large disks. Therefore, the parallel transfer from several inexpensive disks in a RAID system, in which a set of inexpensive disks function as a single logical disk drive, produces better performance than a single large expensive disk (SLED) at a reduced cost.
Unfortunately, when data is stored on more than one disk, the mean time to failure varies inversely with the number of disks in the array. In order to correct for this decreased mean time to failure of the system, error recognition and correction is characteristic of all RAID systems. Generally, each RAID system is organized in six structures commonly referred to as six levels each having a different means for error recognition and correction as described hereinbelow.
In a RAID structure of level 0, data is distributed and stored in all drives in the disk array, taking interests in performance rather than data reliability.
In a RAID structure of level 1, the mirroring, a conventional method of improving the disk performance, has a high cost since all contents of the disk must be stored in a reproduction disk without change. Accordingly, in a database system requiring a large-capacity disk space, only the fifty percent of the disk space can be used. However, the mirroring is the best way to enhance the data reliability because identical data is stored in the reproduction disk. In a RAID structure of level 2, this is used to minimize the cost required to enhance data reliability. The RAID structure of level 2 distributes and stores data in each disk array in bites, and has several test disks using a Hamming Code, besides the data disk, in order to recognize and correct errors.
In a RAID structure of level 3, data is input/output in parallel to/from the drive when input/output is requested once, and parity data is stored in a separate drive. Furthermore, disk spindles are synchronized so as to make all drives simultaneously input or output data. Accordingly, rapid data transmission can be carried out even if parallel input/output is not performed fast. If one drive has an error, the erroneous data can be restored by using the currently operated drive and parity drive even though the total data rate is decreased. The RAID structure of level 3 is used in an application which requires very fast data transmission rate, super computer and image manipulation processors. That is, the RAID of level 3 has a efficiency in a long data block transmission but has a lower efficiency in a short data block transmission which requires fast input/output request. Furthermore, since the data drive is used together with a single drive for redundancy, a device which is smaller than that used in the RAID of level 1 is used but its controller becomes more expensive and complicated.
In a RAID structure of level 4, the parity data is calculated and stored in a separate drive, and data is striped across. The data can be restored when it has error. Its reading performance is similar to that of a RAID of level 1 but its writing is much poorer than the single drive because the parity information must be provided to the single drive. Thus, the RAID structure of level 5 having improved writing performance is supplemented to the RAID of level 4.
In a RAID structure of level 5, data is striped across in each drive array, and parity data is distributed and stored in all drives in order to remove the bottleneck phenomenon when data is written. In this RAID structure, since the data written in all drives must be read in order to calculate the parity when the data is written, its speed is slower. However, it is possible to process the data input/output transmission and to restore data stored in a drive having an error. Accordingly, the RAID structure of level 5 is effective in the recording of long pieces of data, and is also effective in the recording of short pieces of data if an application program gives weight to the data reading or the array design is improved in order to increase the writing performance. Even if the size of the data block is decreased, performance and data availability can be obtained to some degree. Moreover, the RAID structure of level 5 is most effective in terms of cost in comparison with a non-array device.
Among all disk array structures, the RAID structure of level 5 provides a higher reliability with smaller additional cost, and at the same time, makes the parallel disk access possible, resulting in the improvement of data processing rate. Generally, when data writing instruction is received from the host computer for writing in each drive in the RAID structure of level 5, the CPU determines a target location, and transmits the data to a controller where old data and old parity stored in each drive are read. The controller calculates a new parity based on an exclusive OR arithmetic operation, and writes new data and new parity in a predetermined drive. However, when a writing instruction of a short data block is received from the host computer in the RAID structure of 5 level, access of another disk on the strip is brought about which leads to a deterioration of the entire system performance. I have observed that this phenomenon appears in the on-line transaction processing environment having many operation loads. That is, in case of the partial strip writing, old parity and old data are read from a predetermined drive, a exclusive-OR operation is performed to determine new data, and then new parity information and new data are written in the predetermined drive. Two-time reading and writing operations are necessarily required which results in a larger overhead of data write in comparison with a single large expensive drive.
Accordingly, it is therefore an object of the present invention to provide a redundant array of inexpensive disks (RAID) system with an enhanced process performance and a reduced overhead of data write.
It is also an object to provide a RAID system capable of reducing an overhead during a read operation of data recovery information in order to improve its data input/output performance, and a method of caching data recovery information using the memory system.
These and other objects of the present invention can be achieved by a redundant array of inexpensive disks (RAID) system which includes a plurality of defect-adaptive memory devices for sequentially storing information needed for data recovery in a predetermined region of a recording medium in the form of block, and storing data in a region other than the predetermined region. A plurality of caches are connected to the adaptive memory devices to store information blocks needed for data recovery, the information blocks being read from a predetermined memory device. A controller is connected to each adaptive memory device and cache to control the writing and reading of data and information needed for data recovery in each memory device, calculate information needed for recovery of data read from each memory device, and store the information needed for recovery of data calculated in a predetermined cache.
The present invention is more specifically described in the following paragraphs by reference to the drawings attached only by way of example.